In the wet-chemical co-precipitation procedure for the preparation of composition-modified barium titanate powder, it is desirable to remove impurities from the starting materials that are deleterious to the performance of the end product. An example is the barium nitrate [Ba(NO3)2] precursor in which sodium (Na+), potassium (K+), and strontium (Sr2+) ions are particularly undesirable impurities, the first two being mobile ions under an applied electric field, and the third suppressing the relative permittivity.